Water tanks that are used, for example, for water softeners have generally a cylindrical shape wherein the top is closed with a convex dome having for example, three pipe fittings, one larger than the other two, and a concave bottom dish with a cylindrical flange inserted into the end of the tank cylinder and welded thereto. Through the larger fitting, the tank is filled with an ion-exchange compound that exchanges calcium ions found in hard water with sodium ions to make the water soft. Therefore, with the larger fitting suitably plugged, hard water is made to flow into one smaller fitting through the ion exchange compound so that the water exiting from the other smaller fitting is what is normally classified as soft water. After a quantity of water, depending on its degree of hardness, flows through the ion-exchange compound, the compound must be reactivated to replenish the sodium ions and to remove the calcium which is now a salt compound trapped within the tank. This is done by flushing a brine solution through the tank and then rinsing out the excess brine. Naturally, with the presence of active ions such as sodium, the tanks being steel will corrode and the maximum corrosion inherently occurs at the bottom of the tank forming holes in the bottom dish and the cylindrical side. The holes in the cylindrical side are usually within one-quarter inch of the region where the end of the cylinder is welded to the bottom dish. Up to now, one would attempt to repair the tank by welding or brazing these holes, hoping to extend the life of the tank since the rest of the tank was relatively free of corrosion. However, the advanced stage of corrosion at the bottom soon formed other leaks. One could see that if the bottom dish was replaced, the tank life expectancy could be the same as a new one. However, the bottom dish being concave extends an appreciable distance into the tank, if one attempts to saw off the bottom with a saw, it has to be placed above the region of the bottom dish since the curvature of the dish would prevent the saw from cutting through it, causing the saw to bind. This would greatly reduce the volume of the repaired tank and therefore it would have to be replaced more frequently than the nonrepaired ones. Machining off the bottom dish at the weldhead is also not practical because the tanks are relatively out of round. Chipping off the weld to remove the bottom dish would be costly however these operations would preserve substantially the original tank volume.
Assuming a person employing the prior art removes the bottom dish by chipping the weld, the open tank would be sandblasted internally by conventional means before a new bottom dish is installed. The bottom dish is preferably concave with a cylindrical flange extending therefrom, and the tank, while in service, rests on the flange. Since, as mentioned above, the in and out water fittings or connections are made at the top and since the tanks must be interchangeable, the tanks should all be of the same height. The cylindrical flange on the bottom dish has an outside diameter of such a size that it forms a snug fit within the cylindrical wall of the tank. Up to now, to maintain the standard height, one has to force the dish into the tank and then measure its height. If the height is too great, he would push the dish further in and if too small, he would have to pull the dish out, consuming time in the operation and increasing costs. When the correct height is attained, the dish is welded to the cylinder and tested for tightness. The interior of the tank must be coated to prevent corrosion. Since the interior of the tank is now only accessible through the pipe fittings on the top, up to now a uniform protective coating of the inside has been difficult to attain. Before my invention, the liquid to coat the tank was poured through a pipe fitting into the tank and sloshed around to wet the interior thereof, and the excess poured off. Obviously this method is wasteful and does not insure a uniform coating.
Since soft water tanks come in several diameters, for example, 61/2 inches, 8 inches and 10 inches, and some tanks have less than three fittings on the top, any equipment employed in removing and replacing the bottom dishes and employed in the other operations should preferably be able to handle all tanks. As mentioned above, the tank heights are required to be uniform because the tanks are interchangeable even between the several diameters.